How the ClickHouse Buffer Engine Holds Writes in RAM and Flushes Them in the Background
Buffer shards writes in RAM, flushes them on a min/max/flush threshold algebra, and restores the block if the destination write fails.
Storage engines
How the ClickHouse Kafka Engine Commits Offsets Only After the Block Is Written
Kafka offsets are committed only after the block has been written to the views, and a cancelled block is rewound to its start offset and replayed.
How the ClickHouse Log Engine Stores Rows in Append-Only Files with a Marks Index
Log stores one .bin per column stream plus a __marks.mrk file of (rows, offset) pairs, and truncates files back to a recorded size after a crash.